Machines such as, for example, dozers, loaders, excavators, motor graders, and other types of heavy machinery typically include a power source linked to a power conversion unit. Such a configuration is used for transmitting torque from the power source to one or more axle assemblies operatively connected to one or more traction devices for movement of the vehicle over one or more supporting surfaces (e.g., the ground). Torque applied at the axle assemblies may result in rotational motion of components associated with the axle assemblies and, in turn, the traction devices. Thus, the machine may be put in motion based on available friction between the traction devices and the supporting surface, among other things.
The transmission of high torques from the power conversion unit to the axle assemblies may result in strain and possible damage to components of the axle assemblies, particularly where friction between the traction devices and supporting surface is high. Such strain and damage can eventually or immediately lead to failure of components associated with the axle assemblies (e.g., gear bending, gear pitting, roller bearing damage, ball bearing damage, etc.) and removal of the machine from operation for repairs.
The torque applied at the axle assembly may vary based on a gear ratio associated with the power conversion unit, and a power output associated with the power source, among other things. For example, in a first gear associated with a machine, greater torque may be provided to the axle assembly than when in a higher gear (e.g., gears 2-4). Therefore, to limit torque, some systems may cause a power source to operate on one or more pre-defined power curves based on a gear selection associated with a machine. For example, when an operator places a machine in first gear, the power source associated with the machine may be “derated” (i.e., caused to operate on a power curve with an apparent reduced maximum power) to a pre-defined sub-optimal power curve below an optimal power curve associated with the power source. Operation on this sub-optimal power curve may continue as long as the gear selection remains first gear. Such operation, while limiting the potential for torque damage to the drive train, may lead to inefficiencies in performance and operator dissatisfaction, among other things. Further, use of each power curve (both optimal and any sub-optimal power curves) may entail certification with environmental regulatory agencies to ensure compliance with applicable emissions regulations. This may result in an expensive battery of compliance testing for each new additional power curve.
One system for limiting power is described in U.S. Patent Pub. 2006/0001224 (the '224 publication) to Bitter et al., published on Jan. 5, 2006. The '224 publication discloses a loading machine with at least one overload protection device with sensors for determining an overload state in the drive train. The '224 publication teaches various embodiments including the use of strain gauges and ground speed sensors, among others, for detecting operational characteristics of a machine. Such signals from the sensors are then used for determining whether the machine is being operated under a critical operating condition, and signals configured to limit the driving power are generated.
Although the system and method of the '224 publication may provide for controlling of driving power based on an overload condition, it requires determining a ground speed and/or the addition of various strain gauges and other sensors for determination of the overload condition. As such, operation of such an overload control may be both under- and over-inclusive, thereby limiting machine power when not necessary and/or failing to limit machine power when desired. In other words, machine performance and/or component life may suffer. Further, the addition of such sensors may add additional expense to production costs, thereby affecting a manufacturer's bottom line.
The present disclosure is directed at overcoming one or more of the problems or disadvantages in the prior art control systems.